The Spectrograph is intended for multiobject spectroscopy up to 75 objects within the BTA field of view with medium spectral resolution. Spectrograph is mounted in Prime Focus of the 6-m Telescope. Main optical parts : fiber optics units, wide field spectrograph. Focal plane images of the objects transferred by quartz fibers (numerical aperture 0.2 and core diameter 200 mkm) into a long slit. Fibers are shorter then 0.5 m in length and transmit near 80 % of light in the spectral range 3700-9600 A. Fibers are organized in block unit with the possibility to change together with mask. Fibers are fixed in the focal plane in a steel mask that has holes to match the positions of the objects under investigation. The diameter of the working field of view is 17'. For manufacturing the mask the coordinates of targets should be measured with an accuracy better than 0.1". The minimum separation between the holes in the mask is 40". The mask has two additional holes to hold a pair of fibers of 3(26") mm in diameter to project the images of stars needed for adjustment the field and guiding. The spectrograph is equipped with a set of diffraction gratings, which realize dispersions 1.35-5 A/px.
The spectrograph parameters
- fibers Diameter 200 mkm (1.7"), number 75 - field of wiew 17 arcmin - spectral range 3600-9600A - dispersion 1.35-5A /px, realized by a set of gratings of 300-1200 g/mm - resolution FWHM ~ 4 px over the entire field of view - collimator off-axis Maksutov f=300 mm, f/3, field of view 7 deg - collimated beam 100 mm - camera Schmidt-Cassegrain f=150 mm, f/1.2, field of view 14 deg - detector CCD TK 1024 1024 x 1024px, 24 x 24 mkm/px, readout noise 3e- - calibration geometrical distortion, flat-field, comparison spectrum Ar-Ne-He,
- total quantum efficiency 4-5% per 5000 A (telescope+spectrograph+detector) - flextures 10 mkm at zenith distances between 10 and 70 deg - scattered light ~2% - recorded data 75 x 1024elements - transmission variations
of data cube elements
~ 20% without reduction, <2% after reduction
The spectrograph is mounted on the universal prime focus adapter which have the TV guiding sytem with 2 arcmin field of view for pointing the object and two moveable probes for offset guiding with 40 arcsec field of view each. Limiting magnitude for pointing mode is near V~20 at 2 arcsecs seeing, and V~18 in guiding probes. Low speed automatical guiding system help the observer to follow the object during the exposition. Limits of setting the guiding probes are 7-11 arcmin in radial direction and ± 4 arcmin tangential direction. Spectrograph and universal prime focus adapter are under remote control. Data acquisition performed by the PC/AT 586 under the LIMA software..
Spectra with S/N~10 of the objects of V~21 could be obtained with spectral resolution ~6-7 A in spectral range 3700-9600 AA during the exposure time of 3600 sec.
Equipment status : experimental equipment. All observations performed with MOFS should be under supervision and in collaboration with Laboratory staff.
(MOFS responsible astronomer - Laboratory Head Dr. S.N. Dodonov,).
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